This invention relates to minimizing torque ripple in electric motors.
Torque ripple in conventional permanent magnet motors is problematic in that users of devices employing such motors may find the movement of the device, associated with torque ripple, annoying. This is the case with electric assist power steering systems using permanent magnet motors. While the motors perform the intended job of reducing steering effort in a reliable manner, the operator of a vehicle having such system may be able to feel the torque ripple in some situations. Since vehicle manufacturers are constantly attempting to gain consumer interest by avoiding undesirable conditions it is well to reduce torque ripple to levels not detectable by the ordinary human operator.
Disclosed is a system of reducing torque ripple wherein two sets of three Hall sensors are used to provide information on the position of the motor rotor. The three Hall sensors in each set are displaced 120 electrical degrees. The two sets are displaced T electrical degrees apart so as to minimize torque ripple. It is found that torque ripple can thus be reduced to 3% to 5% with no significant change in cogging torque.